Cooler bypass valve assembly for hydraulic system return circuit

A cooler bypass valve assembly for a hydraulic oil return circuit, comprising:

• an unloading valve configured to allow hydraulic oil to flow from a control circuit return line to a hydraulic oil tank if a pressure of hydraulic oil in the control circuit return line exceeds a first threshold;
• a backpressure valve configured to allow hydraulic oil to flow from the control circuit return line to an oil cooler inlet line if the pressure of hydraulic oil in the control circuit return line exceeds a second threshold, wherein the first threshold is greater than the second threshold;
• and
• an orifice configured to limit the flow of hydraulic oil through the backpressure valve;
• the cooler bypass valve assembly controlling flow by at least one of:
• limiting the flow of hydraulic oil through the backpressure valve into the oil cooler inlet line to be between 20% and 40% of the total flow through the control circuit return line;
• making a diameter of the orifice 50-70% of a diameter of the control circuit return line or 30-45% of a diameter of a bore of the backpressure valve;
• and
• setting the pressure of the first threshold to be twice the pressure of the second threshold.

A hydraulic return circuit system, comprising:

• a hydraulic oil tank;
• an oil cooler;
• a control circuit return line;
• an unloading valve configured to allow hydraulic oil to flow from the control circuit return line to the hydraulic oil tank if a pressure of hydraulic oil in the control circuit return line exceeds a first threshold;
• a backpressure valve arranged for parallel fluid flow with the unloading valve and configured to allow hydraulic oil to flow from the return line to the oil cooler through an oil cooler inlet line if a pressure of hydraulic oil in the control circuit return line exceeds a second threshold, wherein the first threshold is greater than the second threshold;
• an orifice configured to limit the flow of hydraulic oil through the backpressure valve;
• a shutoff solenoid configured to prevent the backpressure valve from opening if a temperature of the hydraulic oil is below a threshold temperature;
• and
• a relief valve on the oil cooler inlet line configured to direct hydraulic oil to the hydraulic oil tank if a pressure in the oil cooler inlet line is greater than a relief valve pressure threshold, the relief valve being located downstream of the backpressure valve.